Transmission for vehicle

ABSTRACT

A transmission for a vehicle may include a first input shaft continuously receiving torque from a power source and having a first input transfer gear thereon, a second input shaft selectively receiving torque from the power source through a clutch and having a second input transfer gear thereon, a coupling member configured to allow or restrict rotation of the first input transfer gear relative to the first input shaft, using a difference in rotational speed between the first input shaft and the first input transfer gear, a first countershaft and a second countershaft each having an output transfer gear to engage with the first input transfer gear and the second input transfer gear, and coupling devices selectively coupling the output transfer gears to corresponding countershafts and allowing torque from the power source to be transmitted to a desired shift gear.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2015-0066626, filed May 13, 2015, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission for a vehicle and, moreparticularly, to a transmission for a vehicle that reduces deteriorationof shifting ability, including a backward pulling effect when shifting.

2. Description of Related Art

An automated manual transmission can provide convenience for a driver,similar to an automatic transmission, by providing an automatic shiftingby means of an actuator while a vehicle is driven and can contribute toimproving fuel efficiency of a vehicle while maintaining powertransmission efficiency higher than an automatic transmission.

However, for an automated manual transmission based on a synchro-meshtype shifting mechanism, there is necessarily a period where power froman engine is disconnected while automatic shifting is performed by anactuator that shifts gears, so torque is decreased and the shiftingability is deteriorated resulting in, for example, a backward pullingeffect of the vehicle when shifting.

In order to solve these problems, a technology of selectivelytransmitting power from an engine to a shifting mechanism or an outputshaft, depending on the driving states of a vehicle, by providing aplanetary gear set between the engine and the shifting mechanism hasbeen proposed.

Prior art technology requires two monitors to reduce deterioration ofshifting ability, so the manufacturing cost and weight of a transmissionincrease.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing atransmission for a vehicle that reduces a deterioration of shiftingability, including a backward pulling effect when shifting.

According to various aspects of the present invention, a transmissionfor a vehicle may include a first input shaft continuously receivingtorque from a power source and having a first input transfer gearthereon, a second input shaft selectively receiving torque from thepower source through a clutch and having a second input transfer gearthereon, a coupling member configured to allow or restrict rotation ofthe first input transfer gear relative to the first input shaft, using adifference in rotational speed between the first input shaft and thefirst input transfer gear, a first countershaft and a secondcountershaft each having an output transfer gear to engage with thefirst input transfer gear and the second input transfer gear, andcoupling devices selectively coupling the output transfer gears tocorresponding countershafts and allowing torque from the power source tobe transmitted to a desired shift gear by coupling the output transfergears connected to the desired shift gear in the output transfer gearsto a corresponding countershaft in advance or after synchronization inshifting.

The second input shaft may be a hollow shaft and the first input shaftis inserted in the second input shaft.

The coupling member may be a one-way clutch disposed between the firstinput transfer gear and the first input shaft.

The output transfer gears may include a first pre-mesh gear relativelyrotatably disposed on the first countershaft and engaged with the secondinput transfer gear, a first synchro-mesh gear relatively rotatablydisposed on the first countershaft and engaged with the first inputtransfer gear, a second pre-mesh gear relatively rotatably disposed onthe second countershaft and engaged with the second input transfer gear,and a second synchro-mesh gear relatively rotatably disposed on thesecond countershaft and engaged with the first input transfer gear.

Gear ratios between the first and second input transfer gears and theoutput transfer gears on each of the countershafts may be the same.

The coupling devices may include a first coupling device selectivelycoupling the output transfer gears on the first countershaft to thefirst countershaft, and a second coupling device selectively couplingthe output transfer gears on the second countershaft to the secondcountershaft.

The first coupling device and the second coupling device may be providedindividually for the output transfer gears.

The transmission may further comprise an output shaft disposed inparallel with the first countershaft and the second countershaft, and ashifting mechanism including a plurality of pairs of shift gears withdifferent transmission gear ratios on the first countershaft, the secondcountershaft, and the output shaft, and configured to change and outputtorque from the power source through the output shaft by selecting pairsof gears corresponding to speeds of a vehicle, using a synchronizer.

The first input shaft, the second input shaft, and the output shaft maybe coaxially arranged.

Input shift gears for odd-numbered ranges or even-numbered ranges may bedisposed on the first countershaft, other input shift gears except forthe input shift gears on the first countershaft may be disposed on thesecond countershaft, and output shift gears that are paired with theinput shift gears may be disposed on the output shaft.

The flow of torque transmitted through the first input transfer gear issmoothly changed to the desired pair of shift gears through the secondinput transfer gear by a relative rotation action allowed by the one-wayclutch in the process of shifting to the desired range, so deteriorationof shifting ability, including a backward pulling effect when shifting,is prevented.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g., fuel derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example, bothgasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing the entire configuration of anexemplary transmission for a vehicle according to a first embodiment ofthe present invention.

FIG. 2A, FIG. 2B, FIG. 2C, and FIG. 2D are diagrams illustrating aprocess of shifting from an N-range to a 1-range by an exemplarytransmission for a vehicle of the present invention.

FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are diagrams illustrating aprocess of shifting from the 1-range to a 2-range by an exemplarytransmission for a vehicle of the present invention.

FIG. 4 is a diagram showing the entire configuration of an exemplarytransmission for a vehicle according to the present invention.

FIG. 5 is a diagram showing the entire configuration of an exemplarytransmission for a vehicle according to the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

A transmission for a vehicle according to various embodiments of thepresent invention may include largely a first input shaft INPUT1, asecond input shaft INPUT2, a coupling member, a first countershaft CNT1,a second countershaft CNT2, and coupling devices.

Referring to FIG. 1, in detail, the first input shaft INPUT1 isconnected to a power source at a first end and continuously receivestorque from the power source, and a first input transfer gear 3 may befitted on a second end of the first input shaft INPUT1 to rotate withthe first input shaft INPUT1. The power source may be an engine 1 andthe first input shaft INPUT1 can continuously be rotated by torque fromthe engine 1.

The second input shaft INPUT2 is connected to the power source at afirst end through a clutch and selectively receives torque from thepower source, depending on engagement and disengagement of the clutch,and a second input transfer gear 5 is fitted on a second end of thesecond input shaft INPUT2 without relative rotation, so it rotates withthe second input shaft INPUT2.

For example, the first input shaft INPUT1 and the second input shaftINPUT2 may be coaxially arranged, in which the second input shaft INPUT2may be a hollow shaft and the first input shaft INUPT1 may be insertedin the second input shaft INPUT2.

The coupling member, which allows or restricts rotation of the firstinput transfer gear 3 relative to the first input shaft INPUT1 due to adifference in relative speed between the first input shaft INPUT1 andthe first input transfer gear 3, may be a one-way clutch OWCmechanically connecting or disconnecting power, but it may be amechanical device operating in the same principle, a hydraulic part or ahydraulic-mechanical composite device, or a device usingelectric/electromagnetic force.

That is, the coupling member (hereafter, referred to as a ‘one-wayclutch’) is disposed between the first input transfer gear 3 and thefirst input shaft INPUT1 and allows the first input transfer gear 3 torotate only in one rotational direction of the first input shaft INPUT1.

For example, when the rotational speed of the first input shaft INPUT1is larger than the rotational speed of the first input transfer gear 3,the first input shaft INPUT1 forcibly rotates the first input transfergear 3. In contrast, when the rotational speed of the first input shaftINPUT1 is smaller than the rotational speed of the first input transfergear 3, the first input transfer gear 3 rotates at a higher speedrelative to the first input shaft INPUT1.

Two output transfer gears may be disposed on the first countershaft CNT1to engage with the first input transfer gear 3 and the second inputtransfer gear 5, respectively, and similarly, two output transfer gearsmay be disposed on the second countershaft CNT2 to engage with the firstinput transfer gear 3 and the second input transfer gear 5.

The output transfer gears may include a first pre-mesh gear 7 and afirst synchro-mesh gear 9 on the first countershaft CNT1 and a secondpre-mesh gear 11 and a second synchro-mesh gear 13 on the secondcountershaft CNT2.

In detail, the first pre-mesh gear 7 may be relatively rotatablydisposed on the first countershaft CNT1 and may continuously be in meshwith the second input transfer gear 5.

The first synchro-mesh gear 9 may be relatively rotatably disposed onthe first countershaft CNT1 and may continuously be in mesh with thefirst input transfer gear 3.

The second pre-mesh gear 11 may be relatively rotatably disposed on thesecond countershaft CNT2 and may continuously be in mesh with the secondinput transfer gear 5.

The second synchro-mesh gear 13 may be relatively rotatably disposed onthe second countershaft CNT2 and may continuously be in mesh with thefirst input transfer gear 3.

The gear ratios between the first and second input transfer gears 5 andthe two output transfer gears on each of the countershafts may be thesame.

For example, the gear ratios between the first input transfer gear 3 andthe first synchro-mesh gear 9 and between the second input transfer gear5 and the first pre-mesh gear 7 may be the same. Further, the gearratios between the first input transfer gear 3 and the secondsynchro-mesh gear 13 and between the second input transfer gear 5 andthe second pre-mesh gear 11 may be the same.

The gear ratios of the output transfer gears on the first countershaftCNT1 and the output transfer gears on the second countershaft CNT2 arethe same, but may be different.

The coupling devices selectively couple the output transfer gears to thecorresponding countershafts. For example, by the coupling devices, theoutput transfer gears on the first countershaft CNT1 are selectivelycoupled to the first countershaft CNT1 and the output transfer gears onthe second countershaft CNT2 are selectively coupled to the secondcountershaft CNT2.

That is, by coupling output transfer gears connected to a desired shiftgear in the output transfer gears to a corresponding countershaft inadvance or after synchronization in shifting, torque from the powersource can be transmitted to the desired shift gear from the currentshift gear.

The coupling devices may include a first coupling device on the firstcountershaft CNT1 and a second coupling device on the secondcountershaft CNT2.

In detail, the first coupling device selectively couples the outputtransfer gears on the first countershaft CNT1 to the first countershaftCNT1.

The second coupling device selectively couples the output transfer gearson the second countershaft CNT2 to the second countershaft CNT2.

The first coupling device and the second coupling device may be providedfor each of the output transfer gears and all types of coupling devicesfor connecting/disconnecting power, including a synchro-mesh typesynchronizer, a dog clutch, a modified dog clutch, a wet/dry clutch, anelectric/electronic wet/dry magnet clutch, a coupling, a fluid coupling,and a spline, may be used as the first and second coupling devices.

For example, the first coupling device may include a first-firstcoupling device S1-1 for coupling the first pre-mesh gear 7 to the firstcountershaft CNT1 and a first-second coupling device S1-2 for couplingthe first synchro-mesh gear 9 to the first countershaft CNT1.

The second coupling device may include a second-first coupling deviceS2-1 for coupling the second pre-mesh gear 11 to the second countershaftCNT2 and a second-second coupling device S2-2 for coupling the secondsynchro-mesh gear 13 to the second countershaft CNT2.

That is, since the output transfer gears are each provided with acoupling device for coupling them to corresponding countershafts, thetime taken to engage/disengage two output transfer gears in shifting isreduced, so the shifting time can be minimized.

The transmission for a vehicle according to various embodiments of thepresent invention may further include an output shaft OUTPUT and ashifting mechanism 15.

The output shaft OUTPUT may be disposed in parallel with the firstcountershaft CNT1 and the second countershaft CNT2. The output shaftOUTPUT may be arranged coaxially with the first input shaft INPUT1 andthe second input shaft INPUT2.

Further, though not shown in the figures, output transmitted to theoutput shaft OUTPUT may be increased or decreased in speed throughanother pair of gears, a planetary gear set, or other transmissionelements and then transmitted to wheels.

The shifting mechanism 15 includes a plurality of pairs of shift gearswith different transmission gear ratios on the first countershaft CNT1,the second countershaft CNT2, and the output shaft OUTPUT and can changeand output torque from the power source through the output shaft OUTPUTby selecting pairs of gears corresponding to the speeds of a vehicle,using a synchronizer.

According to the structure of various embodiments of the presentinvention shown in FIG. 1, input shift gears for odd-numbered ranges oreven-numbered ranges may be disposed on the first countershaft CNT1 andother input shift gears except for the input shift gears on the firstcountershaft CNT1 may be disposed on the second countershaft CNT2.

Output shift gears that are paired with the input shift gears may bedisposed on the output shaft OUTPUT.

For example, when input shift gears for a 1-range, a 3-range, a 5-range,and a 7-range are disposed on the first countershaft CNT1, input shiftgears for a 2-range, a 0-range, a 6-range, and an R-range may bedisposed on the second countershaft CNT2 and output shift gears may bedisposed on the output shaft OUTPUT.

A 1&3-range synchronizer S1&3 may be disposed between the 1-range and3-range input shift gears, a 5&7-range synchronizer S5&7 may be disposedbetween the 5-range and 7-range input shift gears, a 2&4-rangesynchronizer S2&4 may be disposed between the 2-range and 4-range inputshift gears, and a 6&R-range synchronizer S6&R may be disposed betweenthe 6-range and R-range input shift gears.

According to the structure of various embodiments of the presentinvention shown in FIG. 4, it can be achieved by changing thearrangement of the synchronizers and the shift gears of the shiftingmechanism shown in FIG. 1.

For example, the odd-numbered-range and the even-numbered-range inputshaft gears may be disposed on the first countershaft CNT1 and thesecond countershaft CNT2, as shown in FIG. 1, but their positions arechanged. Further, the synchronizers on the first countershaft CNT1 orthe second countershaft CNT2 may be disposed on the output shaft OUTPUT.

According to the structure of various embodiments of the presentinvention shown in FIG. 5, as described above, it can be achieved bychanging the arrangement of the synchronizers and the shift gears of theshifting mechanism.

For example, not only odd-numbered-range input shift gears, but someeven-numbered-range input shift gears may be disposed on the firstcountershaft CNT1 and the synchronizers on the first countershaft CNT1or the second countershaft CNT2 may be moved to the output shaft OUTPUT.

The operation and effect of the present invention are describedhereafter.

A process of shifting from the N-range (neutral) to the 1-range isdescribed with reference to FIGS. 2A to 2D.

The first input shaft INPUT1 is directly connected to the engine 1 whenthe vehicle is started, so the first input transfer gear 3 is rotatedwith the first input shaft INPUT1 by the one-way clutch OWC.

In this state, all the coupling devices and synchronizers in thetransmission are positioned for the neutral state, so load is notapplied to the operation of the engine 1 regardless of whether theclutch is engaged or not.

When shifting to the 1-range is started, as shown in FIG. 2A, before theclutch is engaged, the first pre-mesh gear 7 is coupled to the firstcountershaft CNT1 by the first-first coupling device S1-1 and the input1-range shift gear is coupled to the first countershaft CNT1 by the1&3-range synchronizer S1&3.

In this state, when the clutch is engaged, as shown in FIG. 2B, torquefrom the engine 1 starts to be transmitted through the second inputshaft INPUT2 too, so the torque is transmitted to the first countershaftCNT1 through the second input transfer gear 5 and the first pre-meshgear 7 and the vehicle can run in the 1-range by the pair of the 1-rangeshift gears on the first countershaft CNT1 and the output shaft OUTPUT.

Thereafter, the first synchro-mesh gear 9 is coupled to the firstcountershaft CNT1 by the first-second coupling device S1-2 as shown inFIG. 2C.

That is, when the vehicle runs in the 1-range, as in FIG. 2B, the firstinput shaft INPUT1 and the second input shaft INPUT2 rotate at the samespeed and the first pre-mesh gear 7 and the first synchro-mesh gear 9engaged with the first input transfer gear 3 and the second inputtransfer gear 5 make the same gear ratio. Accordingly, since the firstpre-mesh gear 7 and the first synchro-mesh gear 9 rotate with therotational speeds synchronized, the first-second coupling device S1-2can be safely coupled to the first synchro-mesh gear 9 without damage tothe first synchro-mesh gear 9.

Next, the first-first coupling device S1-1 is decoupled from the firstpre-mesh gear 7, as in FIG. 2D, but the first input shaft INPUT1 isdirectly connected to the engine 1 even though the first pre-mesh gear 7is decoupled, so the torque from the engine keeps being transmitted tothe output shaft OUTPUT through the first input transfer gear 3 and thefirst synchro-mesh gear 9 and the vehicle can keep running in the1-range.

Thereafter, though not shown in the figures, torque from the engine 1keeps being transmitted to the output shaft OUTPUT through the firstinput shaft INPUT1 directly connected to the engine 1 even if the clutchis disengaged, so the 1-range can be maintained.

Next, a process of shifting from the 1-range to the 2-range is describedwith reference to FIGS. 3A to 3D.

When shifting from the 1-range to the 2-range is started, as shown inFIG. 3A, with the clutch disengaged, the second pre-mesh gear 11 iscoupled to the second countershaft CNT2 by the second-first couplingdevice S2-1 and the input 2-range shift gear is coupled to the secondcountershaft CNT2 by the 2&4-range synchronizer S2&4.

In this state, when the clutch is engaged, as in FIG. 3B, torque fromthe engine 1 starts to be transmitted through the second input shaftINPUT2 too, so the torque is transmitted to the second countershaft CNT2through the second input transfer gear 5 and the second pre-mesh gear 11and the vehicle can run in the second range by the pair of the 2-rangeshift gears on the second countershaft CNT2 and the output shaft OUTPUT.

That is, the pair of 1-range shift gears are engaged together with thefirst synchro-mesh gear 9 and the vehicle runs in the 1-range, beforethe clutch is engaged, but a relative rotation action in which the firstinput transfer gear 3 is intended to rotate at a higher speed than thefirst input shaft INPUT1 by the difference in gear ratio between thepair of 2-range shift gears and the pair of 1-range shift gears when theclutch is engaged and the relative rotation action is allowed by theone-way clutch OWC.

Accordingly, the flow of torque transmitted to the first countershaftCNT1 through the first input transfer gear 3 when the vehicle runs inthe 1-range smoothly changes to the second countershaft CNT2 through thesecond input transfer gear 5 by the relative rotation action allowed bythe one-way clutch OWC in the process of shifting to the 2-range, sodeterioration of shifting ability, including a backward pulling effectof a vehicle in shifting, is prevented.

Thereafter, the second synchro-mesh gear 13 is coupled to the secondcountershaft CNT2 by the second-second coupling device S2-2 as in FIG.3C.

That is, when the vehicle runs in the 2-range, as in FIG. 3B, the firstinput shaft INPUT1 and the second input shaft INPUT2 rotate at the samespeed and the gear ratios between the second pre-mesh gear 11 and thesecond synchro-mesh gear 13 engaged with the first input transfer gear 3and the second input transfer gear 5 make the same gear ratio.Accordingly, since the second pre-mesh gear 11 and the secondsynchro-mesh gear 13 rotate with the rotational speeds synchronized, thesecond-second coupling device S2-2 can be safely coupled to the secondsynchro-mesh gear 13 without damage to the second synchro-mesh gear 13.

Next, the second-first coupling device S2-1 is decoupled from the secondpre-mesh gear 11, as in FIG. 3D, but the first input shaft INPUT1 isdirectly connected to the engine 1 even though the second pre-mesh gear11 is decoupled, so the torque from the engine 1 keeps being transmittedto the output shaft OUTPUT through the first input transfer gear 3 andthe second synchro-mesh gear 13 and the vehicle can keep running in the2-range.

Thereafter, though not shown in the figures, torque keeps beingtransmitted to the output shaft OUTPUT through the first input shaftINPUT1 directly connected to the engine 1 even if the clutch isdisengaged, so the 2-range can be maintained.

Further, the other ranges can be achieved in the processes of shiftingdescribed above.

As described above, according to the present invention, the flow oftorque transmitted through the first input transfer gear 3 is smoothlychanged to the desired pair of shift gears through the second inputtransfer gear 5 by the relative rotation action allowed by the one-wayclutch OWC in the process of shifting to the desired range, sodeterioration of shifting ability, including a backward pulling effectof a vehicle in shifting, is prevented.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A transmission for a vehicle, comprising: a first input shaft continuously receiving torque from a power source and having a first input transfer gear thereon; a second input shaft selectively receiving torque from the power source through a clutch and having a second input transfer gear thereon; a coupling member configured to allow or restrict rotation of the first input transfer gear relative to the first input shaft, using a difference in rotational speed between the first input shaft and the first input transfer gear; a first countershaft and a second countershaft each having an output transfer gear to engage with the first input transfer gear and the second input transfer gear; and coupling devices selectively coupling the output transfer gears to corresponding countershafts and allowing torque from the power source to be transmitted to a desired shift gear by coupling the output transfer gears connected to the desired shift gear in the output transfer gears to a corresponding countershaft in advance or after synchronization in shifting.
 2. The transmission of claim 1, wherein the second input shaft is a hollow shaft and the first input shaft is inserted in the second input shaft.
 3. The transmission of claim 1, wherein the coupling member is a one-way clutch disposed between the first input transfer gear and the first input shaft.
 4. The transmission of claim 1, wherein the output transfer gears include: a first pre-mesh gear relatively rotatably disposed on the first countershaft and engaged with the second input transfer gear; a first synchro-mesh gear relatively rotatably disposed on the first countershaft and engaged with the first input transfer gear; a second pre-mesh gear relatively rotatably disposed on the second countershaft and engaged with the second input transfer gear; and a second synchro-mesh gear relatively rotatably disposed on the second countershaft and engaged with the first input transfer gear.
 5. The transmission of claim 1, wherein gear ratios between the first and second input transfer gears and the output transfer gears on each of the countershafts are the same.
 6. The transmission of claim 1, wherein the coupling devices include: a first coupling device selectively coupling the output transfer gears on the first countershaft to the first countershaft; and a second coupling device selectively coupling the output transfer gears on the second countershaft to the second countershaft.
 7. The transmission of claim 6, wherein the first coupling device and the second coupling device are provided individually for the output transfer gears.
 8. The transmission of claim 1, further comprising: an output shaft disposed in parallel with the first countershaft and the second countershaft; and a shifting mechanism including a plurality of pairs of shift gears with different transmission gear ratios on the first countershaft, the second countershaft, and the output shaft, and configured to change and output torque from the power source through the output shaft by selecting pairs of gears corresponding to speeds of a vehicle, using a synchronizer.
 9. The transmission of claim 8, wherein the first input shaft, the second input shaft, and the output shaft are coaxially arranged.
 10. The transmission of claim 8, wherein input shift gears for odd-numbered ranges or even-numbered ranges are disposed on the first countershaft, other input shift gears except for the input shift gears on the first countershaft are disposed on the second countershaft, and output shift gears that are paired with the input shift gears are disposed on the output shaft. 